The present invention relates to ways and means for effectively lowering the degree of elevated temperature to which the electronic panel and controls of an oven are subjected, in case of a domestic cooking/baking oven which has a pyrolitic-type self-cleaning cycle or mode of operation, e.g. during which the temperature of the oven cavity is raised to about 550.degree. C. for the purpose of carbonizing or burning-off encrustations and spills from the internal, bounding surface of the oven cavity.
Various previous U.S. patents are pertaining to cooling air flow path(s) inside a domestic cooking or baking oven in order to limit temperature elevation.
U.S. Pat. No. 4,354,084 HUSSLEIN relates to a double built-in baking oven unit which avoids intense heat development in the upper part of the housing. The upper oven is a microwave oven.
Cooling-air channels are located between the housing and the ovens. Inlet and outlet openings are disposed above the controls of the ovens and connected to a lower cooling air inlet opening located at a lower limit of the housing below the lower baking oven through a blower. Shielding plates are disposed both above and below the lower baking oven and are connected to lateral and rear shielding walls in order to form cooling-air channels.
The space formed in a built-in furniture unit and the shielding plates and walls are used as cooling-air channels.
The upper edge of the control panel is bordered by a ventilating strip provided with a hot-air outlet opening connected to a large enclosed hot-air exhaust channel or duct. A cooling air inlet opening extends approximately one third of the length of the strip and is connected through the microwave generator to one entry of the suction part of the blower so that the blower may directly draw the ambient air as cooling air from the outside. This cooling air current intensively cools the microwave generator.
The reduction of temperature comes from the long distance between the oven and the control panel over the microwave oven. It is well known that microwave ovens do not produce a lot of hot air because of microwave heating effect comes from molecule vibration inside the goods to be cooked. Furthermore the air is considerably mixed with fresh air coming from outside so that the temperature of exhausted air is not so high. Furthermore the exhaust channel is very large so that temperature on the control panel may be under 70.degree. C.
This principal advantage results from using numerous openings for fresh air in conjonction with the above said special type of air guidance. This arrangement is sufficient in the case of the double oven, one of both is a microwave oven but will be completely unefficient in the case of a single pyrolytic self-cleaning oven.
U.S. Pat. No. 4,331,124 SEIDEL relates to a gas-fueled oven capable of assuming safely high temperatures such as occur during pyrolytic self-clean cycles. According to this invention a blower is strategically positionned so as to provide flow of cooling air to the walls and the components. Exhaust channel opening is positionned above the control panel, the fresh air is sucked in from under the control panel. The fresh air flow and the hot air flow are mixed before evacuation so that temperature is quite reduced. This kind of method which consists in sucking in fresh air under the control panel and blowing it after mixing with hot air is quite logic and of course obvious. The control panel is not too much heated because of hot air escaping above its upper edge. Furthermore this kind of control panel is not provided with electronic components.
U.S. Pat. No. 4,375,213 KEMP relates to a pyrolytic self-clean gas-fueled built-in oven having means for passing cooling air over the heated walls. This kind of solution to overcome the problem of overheating during pyrolytic phase is particular to gas-fueled ovens. Of course the solution is achieved by exhausting the hot combustion products through an opening located below and between cooling air exhaust openings so that hot combustion air will upon rising mix with the exhausted cooling air outside the enclosure.
Separate exhaust openings for hot combustion air are located under the two superposed channels of exhausted cooling air.
This kind of disposition is typical of ovens provided with gas burners but will not be useful in case of an electronic control panel located in the upper part of the enclosure because temperature in this region is still too high for electronic components.
These days many household cooking/baking ovens are provided with electronic controls, e.g. which include semi-conductor chips, integrate circuits, photodiode displays and the like, which are designed to operate within a limit range of environmental temperature, and which may become destroyed, degraded or inoperative if subjected to too high a temperature for too long a length of time. Often, such electronic controls are not manufactured by the manufacturer of the oven; rather the oven manufacturer often buys them more or less as a standard item from an outside supplier. In such instances, the controls may be furnished by the supplier together with a set of conditions of use, which, if not observed, would void the supplier's guarantee to the oven manufacturer as to the fitness and freedom from defects, of such controls. The controls manufacturers and electronic components manufacturers specify that the average control components and the control panel shall not be subjected to a temperature of more than 60.degree. C.
Quite often, manufacturers of household ovens contemporaneously produce one or more series of various ovens with a range of features for sales at various price levels and to users with various needs and inclinations. Accordingly, it is quite common for a domestic cooking/baking oven manufacturer to offer models of oven having a self-cleaning mode of operation, e.g. a pyrolytic cleaning cycle. In such a case, the model with that feature would likely have additional control circuits and a vertical opening or exhaust of the cooking/baking cavity for very high air temperature which must be actuated in order to initiate control and carry out the self-cleaning cycle.
For reasons of economy, such oven manufacturers would highly prefer to use all electronic components of the controls, including the electronic controls of a common and average kind on their self cleaning oven. The trouble is, that with heretofore conventional mechanical designs of pyrolytic self-cleaning type domestic cooking/baking ovens, the temperatures are likely to become so high, even in the relatively external, relatively out-in-front or up-on-top usual location of such controls, that the controls and electronic components manufacturer's specified upper limit for environmental temperature would be exceeded. Accordingly, heretofore the oven manufacturers have had to choose among the not fully satisfactory alternatives of taking a chance on using electronic components which might fail due to the excess heat; using a non-standard, more rugged design of electronic controls for one or both models, at greater expense; or, using mechanical or electromechanical controls which seem not so versatile or up-to-date to the consumer and which do not work properly under high temperature conditions.
One might think that the usual openings and crevices between the elements of a mass produced oven would be such as to provide adequate ventilation for the controls in such an instance, but always, such is not sufficient. In case of pyrolytic self cleaning operational mode ovens conventional ventilation even powerfull is not sufficient to eliminate problems.
One might also think that the problem could be solved another way, that is, by attempting to thermally insulate the controls instead of by trying to ventilate them. However, this way is not possible. The insulation even thick would never be sufficient during pyrolytic self-cleaning operation because of the high tempereature inside the oven cavity forcing the heated air to escape through the upper exhaust provided with a catalytic cartridge and being finally ejected near the control panel and near the electronic components housing.